The present invention relates to gas turbine engines, and more particularly, to engines with a fan drive gear system having tapered roller bearings.
The rotating shafts and other rotating turbomachinery of gas turbine engines are supported from a non-rotating structure by arrays of anti-friction bearings including tapered roller bearings. In many engines, anti-friction bearings are enclosed in bearing compartments with small envelopes that circumscribe the engine shaft.
In engines with a fan drive gear system, a fan shaft connects a forward-most spool of the engine to a fan. However, due to envelope constraints, the fan shaft is relatively short making it susceptible to instability. In general, because of the relative shortness of the fan shaft, an assembly of tapered roller bearings is used to support the fan shaft in two locations along its length to provide for greater shaft stability (i.e. to increase the wheelbase length of the fan shaft). A spring load must be maintained between the tapered roller bearings to keep the rollers in contact with the raceways. Unfortunately, the spring load applied to these tapered roller bearings in the prior art has either been too stiff in the axial direction (along the engine centerline) to easily accommodate variation due to component tolerances or are not accommodating of bearing flexure in the radial direction so as to allow for proper operation and motion of a squeeze film damper without causing excessive bearing wear.